Conventionally, a contact lens is provided with an identifying mark in the form of letters and figures, symbols, patterns, etc., principally for easy distinction, at a time of wearing, between the front and back surfaces of the lens or between lenses for the left and right eyes, and/or indicating the specifications and/or maker of the lens, for instance.
Various methods have been adopted for marking the ophthalmic lens with the above-mentioned letters, figures, symbols, and patterns. For example, there are known printing methods, in which marks are transferred on the lens surfaces, i.e., on the back surface (base curved surface) and/or the front surface (front curved surface), by using an ink, which is obtained by dissolving or dispersing a dyestuff such as a dye or a colorant in an organic medium. There are also known laser radiation marking methods, in which desired marks are printed or engraved by using a laser.
However, with regard to the mark formed by the former printing method, there are anxieties that the dyestuffs of the mark may be flowed off, discolored, or peeled off due to various treatments repeatedly conducted on the lens, such as cleaning of the lens by rubbing and repetitive disinfection. Moreover, there is a problem that the printing of the mark, after the contact lens has been manufactured, requires many process steps, whereby the marking method is troublesome.
Meanwhile, the mark formed by the latter laser marking method is not easily readable. In addition, as the mark is made by forming grooves or recesses on the lens surface by the laser radiation, the thickness of the portions of the lens, which portions are subjected to the laser radiation, is inevitably reduced, or the lens material is denatured by the laser radiation. In either case, the mechanical strength of the ophthalmic lens is reduced. Further, deposits are likely to accumulate in the grooves or recesses made by the laser radiation, which may cause a trouble such as making a hotbed for breeding bacteria.
JP-A-2-134612 discloses a method of manufacturing a molded color contact lens, wherein the contact lens has a transparent central optical portion and a colored iris portion, which surrounds the central optical portion. In JP-A-2-134612, a predetermined portion of a molding surface of a mold is covered with a colored substance in the liquid state, so as to form a colored film. Subsequently, a liquid for forming a lens is introduced to the mold, and the liquid is polymerized, while the colored film is held to the mold. In this way, there is manufactured a contact lens, wherein the colored film and the lens body is integrated with each other, so that the surface of the colored film forms a part of the outer surface of the lens. Besides, in JP-A-4-265710, there is disclosed a method of manufacturing a contact lens with an iris pattern, wherein at least two different designs are provided on the surface of a mold for an mold assembly for polymerization, and these designs are transferred to the surface of the contact lens, by contacting with the surface of the mold, while the contact lens is molded and cured. In addition, in JP-2000-122004, there is proposed a method of manufacturing a colored contact lens with a colorful appearance, wherein after a dye composition is printed on a concave portion of a mold, a lens material is dropped on the mold, and the mold is subjected for spinning, whereby a semi-spherical surface (convex surface) is formed. In addition, particles of the colorant are dispersed in the lens material, owing to the centrifugal force, whereby the contact lens with the colorful appearance is manufactured.
However, with regard to the methods disclosed in the above-mentioned publications, there are anxieties that: a coloring composition (ink) may be repelled on the mold, when the coloring composition or the ink, which includes the dye or colorant, is printed on the surface of the mold; the dyestuff in the coloring composition may be exuded to the monomer mixture, when the coloring composition printed on the surface of the mold is caused to contact the monomer mixture to provide the polymer to form the contact lens, whereby the color of the coloring composition may be blurred and the mark formed on the contact lens may be unclear; the marker portion and the lens body cannot be sufficiently integrated to each other, whereby the marker portion remains on the mold; or an insufficient transfer of the marker portion, wherein the marker portion is easily removed from the contact lens, even if the marker portion is transferred. These problems cause to lower a yield of the product, and therefore, there are still needed further improvements.